The car will do active cooling when parked in the sun on a very hot day. It will run the AC to keep the pack under some upper limit even when not plugged in.
Up until the point when the pack computer has to make a choice...
Is it better to drain the last bit of pack energy to keep the cells cool, or better to leave some charge and let them get warmer than optimal?
Best to leave it plugged in if the car is parked for extended periods in extreme temps.